6.9. Enable Color Management

Also, if you've selected to
display the image's assigned ICC color profile on the title or status bar,
unchecking Enable Color Management prints
the phrase "not color managed" to the title or status bar in place
of the previously assigned color profile.

注意

Enable Color Management is checked by default. It's best to leave
this option checked.

6.9.1. Activating the command

You can access this command from the image menu bar through
Image → Color Management → Enable Color Management.

6.9.2.
Use Notes regarding unchecking
Enable Color Management

The best possible advice is to never uncheck Enable Color Management.

6.9.3.
What does GIMP do when
Enable Color Management is unchecked?

When you uncheck the option to
Enable Color Management, GIMP does
two things:

Whatever ICC profile is currently assigned to the image
file is at least temporarily stored (pending subsequent editing,
Precision, and Color Management actions), but isn't used.
And then a built-in GIMP profile is assigned in place of the previously
assigned ICC profile:

If the image is at Perceptual gamma (sRGB) precision,
the ICC profile "GIMP built-in sRGB" is assigned.

If the image is at Linear light precision, the ICC
profile "GIMP built-in Linear sRGB" is assigned.

You can confirm that one of GIMP's built-in sRGB color spaces has
been assigned by checking "Image/Image Properties/Color Profile".

If you have set up the title or status bar to show the
image's color space, then the title or status bar will display a message
that the image is "not color managed". In reality the image is
still color managed, but now the image is color managed
"as if" it were in one of GIMP's built-in sRGB color spaces instead of
whatever color space it's actually in.

6.9.4.
When Enable Color Management
is unchecked, what happens to the image
and the image appearance?

注意

Assigning a new profile to an image doesn't change the image's
actual channel values. Assigning a new ICC profile only changes the meaning
of the channel values, which means the image appearance will change (unless
the original and new profile are functionally equivalent).

When Enable Color Management is unchecked,
GIMP assigns one of GIMP's
built-in sRGB profiles to the image. Assigning a new ICC profile to an image
doesn't change the image's channel values, but it does more or less
drastically change the image's appearance:

If the image was already in one of GIMP's built-in color
spaces (or if the assigned ICC profile is a profile that is functionally
equivalent to the assigned GIMP built-in sRGB profile) then the image's
appearance will not change.

If the image was not already in one of GIMP's built-in
color spaces (and is not in a color space that is functionally
equivalent to the assigned GIMP built-in sRGB profile),
the image's appearance will change more
or less drastically depending on three things:

What GIMP Precision channel encoding —
Linear light or Perceptual gamma (sRGB) — the image was in
before the Enable Color Management box was unchecked.

How far the image's originally assigned ICC profile's
channel encoding ("TRC") is from the GIMP Precision channel encoding.

How far the image's originally assigned ICC profile's
Red, Green, and Blue chromaticities are from GIMP's built-in sRGB
chromaticities.

In both screenshots shown below, the image is color
managed: An ICC profile is assigned to the image, and that profile is being
used to send the image colors to the screen.

But in the second screenshot, after unchecking Enable Color
Management, one of GIMP's built-in sRGB profiles has been incorrectly
assigned to the image, so the colors look wrong.

In screenshot 1 below, the image is already in a GIMP built-in sRGB
color space. So unchecking Enable Color Management
makes no difference in the appearance of the image. In this
particular case unchecking Enable Color Management actually makes
no difference at all, except that if you've selected to show the
image's assigned ICC profile in the title or status bar, then instead
of showing the assigned ICC profile, the title or status bar will
show the words "not color managed". But in reality the image is still
color managed:

In screenshot 2 below, the channel encoding of the original profile
matches the GIMP channel encoding (both are linear), but the
LargeRGB-elle-V4-g10.icc profile chromaticities don't match the GIMP built-in
sRGB chromaticities. So after unchecking
Enable Color Management, the tonality
is correct but the colors are wrong. The image is still color managed,
but it's color managed using the wrong ICC profile:

小心

If your image's originally assigned ICC profile doesn't have the same
channel encoding and chromaticities as the GIMP built-in sRGB profile, and
you uncheck and then immediately change your mind
and recheck Enable Color Management,
the originally assigned ICC profile
will be reassigned to your image and your image channel values will be
unchanged.

Otherwise, whether or not you can recover the originally
assigned ICC profile and correct colors for your image depends on what
else you've done between the unchecking and rechecking of
Enable Color Management.

Again, the best possible advice is to never uncheck Enable Color Management.